1. Field of the Invention
The present invention relates an ink jet printing apparatus. Specifically, the present invention relates to a tube pump used in ejection recovery operations for maintaining and recovering an ejection performance of a print head for ejecting ink.
2. Description of the Related Art
FIG. 10 is a plan view of a tube pump in related art described in Japanese Patent Laid-Open No. 2008-49565. In FIG. 10, a first pump tube 325 is coupled to a first cap, and a second pump tube 326 is coupled to a second cap. The first pump tube 325 and the second pump tube 326 are arranged along arc-shaped guide portions 327a and 327b disposed on a pump base 327, respectively. Rollers 331, 332, and 333 press the first pump tube 325 and the second pump tube 326. The rollers 331, 332, and 333 include shaft portions 331a, 332a, and 333a, respectively, and are fit in grooves in a roller holder 330.
When the roller holder 330 is rotated in the direction of the arrow A in FIG. 10, the shaft portions 331a, 332a, and 333a of the rollers move while rotating in the grooves of the roller holder 330. With this, the rollers 331, 332, and 333 move to positions where they press the first pump tube 325 and the second pump tube 326. When the roller holder 330 is rotated continuously in the direction of the arrow A in the state where the first pump tube 325 and the second pump tube 326 are pressed, the inside of each of the first pump tube 325 and the second pump tube 326 can be brought into a negative pressure state. Accordingly, ink can be sucked from a print head using the first cap and the second cap.
When the roller holder 330 is rotated in the direction of the arrow B in FIG. 10, the shaft portions 331a, 332a, and 333a of the rollers move in the direction opposite to the above-described direction while rotating in the grooves in the roller holder 330. With this, the rollers 331, 332, and 333 move to positions where they do not press the first pump tube 325 or the second pump tube 326.
The first pump tube 325 and the second pump tube 326 are near each other in introduction portions from the outside of the pump base 327 to the pump base 327. Thus the rollers 331, 332, and 333 are in contact with both the first pump tube 325 and the second pump tube 326 when passing through the introduction portions.
To increase the print speed, the print head has nozzles more than those of a traditional print head. To perform a suction recovery operation for the print head having many nozzles, it is necessary to raise the suction pressure and increase the amount of ink sucked.
The suction pressure can be raised by an increase in the rotational speed of the roller holder. In that case, however, there is a problem that noise of the driving source for the roller holder is increased.
An increase in the inner diameter of each of the pump tubes can increase the amount of reduction in the inner volume of the pump tube when it is pressed by the roller and thus can raise the suction pressure. However, the increased inner diameter of the pump tube leads to increased rigidity of the pump tube, and this makes it difficult to arrange the two pump tubes in positions near each other in the introducing portions to the pump base.
There is a configuration in which a roller holder of a tube pump is rotated by driving of a conveyance motor for driving a conveyance roller for conveying a printing medium. This configuration aims to avoid increase in cost of the apparatus caused by the addition of another driving source for rotating the roller holder. The roller holder rotates in the direction of the arrow B in FIG. 10 in conveyance of the printing medium. The configuration in which the first and second pump tubes are not near each other in the introducing portions has a trouble described below occurring when the rollers pass through the introducing portions together with rotation of the roller holder.
That is, each of the rollers is repelled in the direction of rotation of the roller holder by a reaction force of a first pump tube in contact with the roller before the roller passes through the introducing portion. Because a second pump tube is remote from the first pump tube, the roller repelled by the reaction force of the first pump tube cannot come into contact with the second pump tube. Thus there are technical problems in that the roller may collide with the pump base, the shaft portion of the roller may collide with the groove in the roller holder, and thus noise may occur.